The present invention relates to a thermochemical reactor for extracting gaseous or liquid fuel from a raw material, preferably from biomass, via pyrolytic conversion.
In the light of a forseeable shortage of fossil fuels and the effects of their use on the climate, the public interest in the utilization of sustainable raw materials, i.e., biomass, as an energy source is increasing. One problem that is associated with the use of biomass as an energy source is its water content which is usually high. Fresh vegetable biomass generally has a water content that is so high that the attainable yield of fuel does not cover the costs and energy required to harvest and haul the biomass to a stationary pyrolysis unit. If it is possible to harvest biomass when it is dry, the ratio of yield to cost is better since the costs to transport the high water content are eliminated. Climatic conditions must be favorable in order for this to take place, however, and it is generally practical for use only with annual plants which die off and dry on the field after the fruit ripens. In order to also process fresh biomass cost-effectively, ways must be found to reduce the hauling costs. One approach is to process the biomass into fuel directly in the field. DE 10 2004 003 011 A1 describes, for this purpose, a vehicle that is capable of traveling on fields and includes several installed processing modules, including one used to press juices from harvested plant material, and one used to process the dried substance obtained from the plant material into a fractional raffinate, the fractions of which should consist of gasoline, diesel oil, or heavy oil. No information is provided regarding the design of the latter module.
A thermochemical reactor which may be used to extract fuel from dehydrated plant material in a vehicle that is capable of traveling on fields must be compact and capable of performing the conversion rapidly so that the plant material may be further processed at the same rate at which it is harvested. In addition, it should be possible for the reactor to operate continually.
A method that appears to meet these requirements is ablative flash pyrolysis, in the case of which material to be pyrolyzed is pressed against a hot surface where it chars while the material and the surface move relative to one another. A device for performing ablative flash pyrolysis that includes a contact surface and a pressing device for pressing raw material to be pyrolyzed against the rotationally symmetrical contact surface which is rotatable relative to the raw material is described, e.g., in DE 103 45 842 A1.
In the case of this known device, the contact surface is formed by a disk which rotates about an axis, and the raw material is pressed onto the surface in a direction that is parallel to the axis. The problem results that it is difficult to ensure an even temperature distribution on the disk which is heated by the burner, on its side facing away from the raw material, and that the speed at which the disk and raw material move relative to one another depends on the distance between the contact point and the rotational axis of the disk. To attain a high raw material throughput rate, the largest possible portion of the surface of the disk should be used for the conversion. The greater this portion is, the greater the radius range is across which the contact surface extends, and the more non-uniform the conditions are under which the conversion takes place, thereby making it that much more difficult to control the process.